1. Field of the Invention
The present invention relates to phonograph record reproduction, and in particular to an automatic record changer permitting preprogrammed sound track selection.
2. Brief Description of the Prior Art
Various turntable systems have been proposed which are designed to permit a user to select a certain number of sound tracks to be played. Most recordings are sold in the form of a disc-type phonograph record where a plurality of sound track selections are spaced apart by land areas which include an unrecorded groove to carry the stylus to the next sound track selection. Often, a user of this type of phonograph record will want to hear fewer than all of the sound track selections on the record. One proposal is shown in U.S. Pat. No. 2,952,464 to M. Stimler. However, the system shown is very bulky and requires optical lenses mounted on the end of the tone arm. A later patent to Nakagiri, et al. U.S. Pat. No. 3,368,080 attempts to solve some of the problems encountered by Stimler's system by using two photocells which are spaced apart from one another to facilitate location of a land area. U.S. Pat. No. 3,937,903 to Osann utilizes an electro-optic sensor, including a light emitting diode and a phototransistor to measure reflective light from the record surface in an attempt to define or locate the land areas.
All of these devices are flawed by certain inadequacies with respect to their ability to handle recordings having particular characteristics. For example, Osann attempts to define a predetermined output level for the electro-optic sensor which will signal the appearance of a land area between two sound track portions. However, it has been found that the predetermined level varies greatly from record to record and over various portions of the same record. Thus there is a need for greater reliability in such a system. The present invention is directed to solving the practical problem of surface non-uniformity of commercial recordings.